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International audience; At cryogenic temperature and at the single emitter level, the optical properties of single-wall carbon nanotubes depart drastically from that of a one-dimensional (1D) object. In fact, the (usually unintentional) localization of excitons in local potential wells leads to nearly 0D behaviors such as photon antibunching, spectral diffusion, inhomogeneous broadening, etc. Here, we present an hyperspectral imaging of this exciton self-localization effect at the single nanotube level using a super-resolved optical microscopy approach. We report on the statistical distribution of the traps localization, depth and width. We use a quasi-resonant photoluminescence excitation approach to probe the confined quantum states. Numerical simulations of the quantum states and exciton diffusion show that the excitonic states are deeply modified by the interface disorder inducing a remarkable discretization of the excitonic absorption spectrum and a quenching of the free 1D exciton absorption.

Single photon emission in the near infrared was recently reported in individual carbon nanotubes, either plain or functionalized, with however a moderate quantum yield. Here we use a tunable fiber cavity to enhance light-matter interaction, using the so-called Purcell effect to boost the performances of the single photon source in view of applications in quantum telecommunications. Preferential excitation conditions building on localized excited states, both for plain and functionalized nanotubes, are considered and the performances of the sources in terms of purity, brightness and indistinguishability are discussed.

Carbon nanotubes have emerged as original single photon source in the near IR and in the telecom bands. To further control their emission rate and directionality, individual carbon nanotube can be coupled to a high Q and small mode volume cavity (Purcell effect). Due to the 1D geometry of carbon nanotube, the coupling between localized exciton and acoustic phonon is particularly strong. This coupling can be used as an additional degree of freedom in cavity coupled single emitters; it brings a very rich physics involving non-markovian decoherence, tripartite coupling, and asymmetric energy exchange... In particular the coupling to phonon can be used to “force” the nanotube to emit preferentially at the cavity frequency rather than at its intrinsic transition frequency.. We implemented this approach to realize a widely tunable single photon source. Jeantet et al, PRL 116, 247402 (2016) Jeantet et al, Nano Lett. 17, 4184 (2017) He et al , Nat. Mat. 17, 663 (2018) Chassagneux et al PRB 97, 205124 (2018)

We use a combination of hyperspectral superlocalization microscopy and excitation photoluminescence spectroscopy techniques to study the localization of one-dimensional excitons in pristine and functionalized single wall carbon nanotubes at low and room temperature. Using numerical simulations, we interpret the nearly resonant excitation spectra either in terms of excited trapped states leading a selective excitation of a trap or in terms of delocalized one dimensional excitonic states. We discuss the implications of this localization for the use of carbon nanotubes as quantum-light emitters. Raynaud et al. Nano Lett. 19, 7210 (2019)

We develop a theoretical frame to investigate the spectral dependence of the brightness of a single-photon source made of a solid-state nanoemitter embedded in a high-quality factor microcavity. This study encompasses the cases of localized excitons embedded in a one-, two-, or three-dimensional matrix. The population evolution is calculated based on a spin-boson model, using the noninteracting blip approximation. We find that the spectral dependence of the single-photon source brightness (hereafter called spectral efficiency) can be expressed analytically through the free-space emission and absorption spectra of the emitter, the vacuum Rabi splitting, and the loss rates of the system. In other words, the free-space spectrum of the emitter encodes all the relevant information on the interaction between the exciton and the phonon bath to obtain the dynamics of the cavity-coupled system. We compute numerically the spectral efficiency for several types of localized emitters differing by the phonon bath dimensionality. In particular, in low-dimensional systems where this interaction is enhanced, a pronounced asymmetric energy exchange between the emitter and the cavity on the phonon sidebands yields a considerable extension of the tuning range of the source through phonon-assisted cavity feeding, possibly surpassing that of a purely resonant system.

At cryogenic temperatures, the photoluminescence (PL) spectrum of nano-emitters may still be significantly broadened due to interactions with the environment. The interplay of spectral diffusion (SD) and phonon broadening in this context is still a debated issue. Singlewall carbon nanotubes (SWNTs) are a particularly relevant system to address this topic as they show intense spectral diffusion and undergo a high exciton-phonon coupling due to their one-dimensional geometry. Here, we investigate the correlations between the spectral diffusion of the main line and that of the wings in SWNTs quantitatively and demonstrate that the photoluminescence spectrum undergoes spectral jumps as a whole, without distortions. This behavior suggests that the spectral shape of SWNT PL is defined by exciton-phonon interactions and that spectral diffusion results in an additional flat broadening. The methodology developed here can be used to investigate a broad range of non-Lorentzian emitters undergoing spectral diffusion.

Microfluidic lenses are relevant optical components for sensing application in lab-on-a-chip devices, guaranteeing a robust alignment of the elements, a high level of compactness and tunable optical properties. In this work we describe an innovative integrated in-plane microfluidic lens. The device shows both an optimized shape capable of reducing spherical aberrations and periodically tunable optical properties. Indeed through the combination of the lens with a droplet generator module, we have been able to obtain an integrated optofluidic modulator capable of both on-demand on/off switching and periodic modulation of light. The device possesses a simple 3D geometry, which has been realized by exploiting the 3D capability of the femtosecond laser micromachining fabrication technique.

International audience; Condensed-matter emitters offer enriched cavity quantum electrodynamical effects due to the coupling to external degrees of freedom. In the case of carbon nanotubes, a very peculiar coupling between localized excitons and the one-dimensional acoustic phonon modes can be achieved, which gives rise to pronounced phonon wings in the luminescence spectrum. By coupling an individual nanotube to a tunable optical microcavity, we show that this peculiar exciton–phonon coupling is a valuable resource to enlarge the tuning range of the single-photon source while keeping an excellent exciton-photon coupling efficiency and spectral purity. Using the unique flexibility of our scanning fiber cavity, we are able to measure the efficiency spectrum of the very same nanotube in the Purcell regime for several mode volumes. Whereas this efficiency spectrum looks very much like the free-space luminescence spectrum when the Purcell factor is small (large mode volume), we show that the deformation of this spectrum at lower mode volumes can be traced back to the strength of the exciton-photon coupling. It shows an enhanced efficiency on the red wing that arises from the asymmetry of the incoherent energy exchange processes between the exciton and the cavity. This allows us to obtain a tuning range up to several hundred times the spectral width of the source.

At cryogenic temperature and at the single emitter level, the optical properties of single-wall carbon nanotubes depart drastically from that of a one-dimensional (1D) object. In fact, the (most usually unintentional) localization of the exciton in local potential wells leads to nearly 0D behaviors such as photon antibunching, spectral diffusion, inhomogeneous broadening... Here, we present an hyperspectral imaging of this exciton self-localization effect at the single nanotube level using a super-resolved optical microscopy approach. We report on the statistical distribution of trap depths, size and density. Together with a excitation resolved photoluminescence approach, we show that the excitonic states are deeply modified by the interface disorder inducing a remarkable discretization of the S11 absorption spectrum.

We performed a thorough and quantitative investigation of spectral diffusion at low temperature in carbon nanotubes wrapped in PFO and embedded in a polystyren matrix, a system of interest for applications for quantum light states generation. We show that an intrinsic line shape typical of exciton-acoustic phonon coupling can be traced back down to the µs time-scale, while spectral diffusion yields a feature-less spectral broadening of the zero-phonon line. By tuning physical parameters such as temperature and pump power we investigate the line-shape deformation at several integration time-scales. Finally, we discuss the implications of these optical properties as regards the efficiency of the static and dynamical coupling of carbon nanotube to optical micro-cavities for single photon generation.

Microfluidic lenses are a powerful tool for many lab on a chip applications ranging from sensing to detection and also to imaging purpose, with the great advantage to increase the degree of integration and compactness of these micro devices. In this work we present the realization of such a compact microfluidic lens with reconfigurable optical properties. The technique used to realize the device we present is femtosecond laser micromachining followed by chemical etching, which allows to easily fabricate 3D microfluidic devices with an arbitrary shape. Thanks to that it has been possible to easily fabricate different lens made up by cylindrical microchannel in fused silica glasses filled with liquids with a proper refractive index. The optical properties of these devices are tested and shown to be in a good agreement with the theoretical model previously implemented. Furthermore we have also optimized the design of these microlenses in order to reduce the effects of spherical aberrations in the focal region, thus allowing us to obtain a set of different acylindrical microfluidic lenses, whose validation is also reported. In this work the lens adaptability can be achieved by replacing the liquid inside the microchannel, so that we can easily tune the feature of the focused beam. Thus increasing the possible range of applications of these micro optical elements, as an example we report on the validation of the device as a fast integrated optofluidic shutter.

Carbon nanotubes have recently proven to be promising nano-emitters for future single-photon sources in the telecom wavelengths [1,2,3]. Coupling the nanotube to a micro-cavity brings a invaluable handle to control single-photon emission, regarding the rate, the yield, the directionnality and the extraction. All those features are related to the so-called Purcell effect that results from the interaction of a quasi-two-level system with a high Q and low mode-volume optical cavity. In carbon nanotubes though, the situation is slightly more complex due to the intimate coupling of the excitonic levels with the acoustic phonon bath, resulting in the well-known phonon wings [4]. This additional degree of freedom brings a very rich physics that can be exploited to enlarge the bandwidth of the source in view of multiplexing. A consequence of the non-Markovian decoherence induced by the phonon bath is the asymetry between the phonon-assisted absorption and emission processes. Using those transitions in the Purcell regime can lead to an enhanced single-photon efficiency above the standard limit imposed by the emitter and cavity intrinsic losses. We developped a widely tunable cavity technique, based on laser-engineered optical fibers to investigate this effect. We measure the single-photon emission properties both in the cw and time-resolved modes and explain the strong asymetry of the efficiency with respect to the detuning. [1] A. Jeantet et al., Phys. Rev. Lett. 116, 247402 (2016) [2] S. Khasminskaya et al., Nat. Phot. 10, 727 (2016) [3] X. Ma, et al., Nat. Mat. 10, 671 (2015) [4] F. Vialla et al., Phys. Rev. Lett. 113, 057402 (2013)